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 $71.57   12.200%   $80.3015   $80.30   $80.30   $80.30  
  Purchase #2 $54.58   7.261%   $58.5431   $58.54   $58.55   $58.50  
  Purchase #3 $29.31   11.128%   $32.5716   $32.57   $32.55   $32.60  
  Purchase #4 $229.51   7.819%   $247.4554   $247.46   $247.45   $247.50  
  Purchase #5 $122.76   3.194%   $126.681   $126.68   $126.70   $126.70  
  Purchase #6 $244.54   9.454%   $267.6588   $267.66   $267.65   $267.70  
  Purchase #7 $177.57   13.370%   $201.3111   $201.31   $201.30   $201.30  
  7 purchase totals = $929.84       $1,014.5225   $1,014.52   $1,014.50   $1,014.60