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 $54.71   8.191%   $59.1913   $59.19   $59.20   $59.20  
  Purchase #2 $218.65   6.126%   $232.0445   $232.04   $232.05   $232.00  
  Purchase #3 $243.52   8.862%   $265.1007   $265.10   $265.10   $265.10  
  Purchase #4 $246.75   4.415%   $257.644   $257.64   $257.65   $257.60  
  Purchase #5 $156.61   4.431%   $163.5494   $163.55   $163.55   $163.50  
  Purchase #6 $197.80   7.338%   $212.3146   $212.31   $212.30   $212.30  
  Purchase #7 $53.28   9.444%   $58.3118   $58.31   $58.30   $58.30  
  7 purchase totals = $1,171.32       $1,248.1563   $1,248.14   $1,248.15   $1,248.00