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 $101.41   6.819%   $108.3251   $108.33   $108.35   $108.30  
  Purchase #2 $186.36   8.293%   $201.8148   $201.81   $201.80   $201.80  
  Purchase #3 $103.31   8.254%   $111.8372   $111.84   $111.85   $111.80  
  Purchase #4 $189.84   11.784%   $212.2107   $212.21   $212.20   $212.20  
  Purchase #5 $137.56   10.342%   $151.7865   $151.79   $151.80   $151.80  
  Purchase #6 $204.26   3.135%   $210.6636   $210.66   $210.65   $210.70  
  Purchase #7 $37.35   5.334%   $39.3422   $39.34   $39.35   $39.30  
  7 purchase totals = $960.09       $1,035.9801   $1,035.98   $1,036.00   $1,035.90