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 $169.53   3.804%   $175.9789   $175.98   $176.00   $176.00  
  Purchase #2 $58.87   11.541%   $65.6642   $65.66   $65.65   $65.70  
  Purchase #3 $224.51   9.803%   $246.5187   $246.52   $246.50   $246.50  
  Purchase #4 $212.30   3.284%   $219.2719   $219.27   $219.25   $219.30  
  Purchase #5 $97.85   11.172%   $108.7818   $108.78   $108.80   $108.80  
  Purchase #6 $29.83   5.761%   $31.5485   $31.55   $31.55   $31.50  
  Purchase #7 $230.51   6.313%   $245.0621   $245.06   $245.05   $245.10  
  7 purchase totals = $1,023.40       $1,092.8261   $1,092.82   $1,092.80   $1,092.90