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 $156.43   11.753%   $174.8152   $174.82   $174.80   $174.80  
  Purchase #2 $128.70   3.570%   $133.2946   $133.29   $133.30   $133.30  
  Purchase #3 $171.69   5.263%   $180.726   $180.73   $180.75   $180.70  
  Purchase #4 $215.55   9.414%   $235.8419   $235.84   $235.85   $235.80  
  Purchase #5 $83.51   13.376%   $94.6803   $94.68   $94.70   $94.70  
  Purchase #6 $120.96   8.713%   $131.4992   $131.50   $131.50   $131.50  
  Purchase #7 $96.38   10.524%   $106.523   $106.52   $106.50   $106.50  
  7 purchase totals = $973.22       $1,057.3802   $1,057.38   $1,057.40   $1,057.30