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 $235.52   4.841%   $246.9215   $246.92   $246.90   $246.90  
  Purchase #2 $163.33   4.327%   $170.3973   $170.40   $170.40   $170.40  
  Purchase #3 $101.72   4.421%   $106.217   $106.22   $106.20   $106.20  
  Purchase #4 $247.98   9.607%   $271.8034   $271.80   $271.80   $271.80  
  Purchase #5 $96.56   12.243%   $108.3818   $108.38   $108.40   $108.40  
  Purchase #6 $10.35   9.342%   $11.3169   $11.32   $11.30   $11.30  
  Purchase #7 $118.61   3.340%   $122.5716   $122.57   $122.55   $122.60  
  7 purchase totals = $974.07       $1,037.6095   $1,037.61   $1,037.55   $1,037.60