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 $177.98   8.417%   $192.9606   $192.96   $192.95   $193.00  
  Purchase #2 $68.35   9.799%   $75.0476   $75.05   $75.05   $75.00  
  Purchase #3 $71.52   8.335%   $77.4812   $77.48   $77.50   $77.50  
  Purchase #4 $206.68   11.873%   $231.2191   $231.22   $231.20   $231.20  
  Purchase #5 $247.45   11.677%   $276.3447   $276.34   $276.35   $276.30  
  Purchase #6 $117.62   7.601%   $126.5603   $126.56   $126.55   $126.60  
  Purchase #7 $39.27   11.270%   $43.6957   $43.70   $43.70   $43.70  
  7 purchase totals = $928.87       $1,023.3092   $1,023.31   $1,023.30   $1,023.30