Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $206.87   9.414%   $226.3447   $226.34   $226.35   $226.30  
  Purchase #2 $50.81   13.447%   $57.6424   $57.64   $57.65   $57.60  
  Purchase #3 $172.56   9.425%   $188.8238   $188.82   $188.80   $188.80  
  Purchase #4 $112.52   12.580%   $126.675   $126.68   $126.70   $126.70  
  Purchase #5 $113.97   4.393%   $118.9767   $118.98   $119.00   $119.00  
  Purchase #6 $155.86   11.649%   $174.0161   $174.02   $174.00   $174.00  
  Purchase #7 $232.77   4.330%   $242.8489   $242.85   $242.85   $242.80  
  7 purchase totals = $1,045.36       $1,135.3276   $1,135.33   $1,135.35   $1,135.20